In the art of high power lasers, it is often necessary to focus a high power beam through an aperture having a certain size, thereby blocking undesired optical flux passing along the beam direction at a distance greater than the aperture size. In the prior art, rectangular or triangular cross section apertures have been used, but these suffer from high heat loads caused by the high flux in the optical beams being limited. The high temperatures associated with large amounts of power in the optical beam can cause severe cooling problems for such devices.